Systematic Methodology for Reliability Analysis of Components in Axial Piston Units

Abstract

This paper covers a reliability analysis as a qualitative method, especially focused on axial piston units. The method is based on Fault Tree Analysis (FTA) and results in risk and reliability assessment at the components level. Especially, the development of the reliability assessment as a methodical tool is the core of the paper. Moreover, the FTA is combined with the industrial standard method known as Design Failure Mode Effects Analysis (DFMEA) which is typically used in the development phase of the design. The evaluation and the usability of the FTA methodology is analyzed in connection with field data. Thus, the deviation of the theoretical valuation from the field data was utilized as a success indicator of the method. The analysis of the fault spreading covers the assessment of component faults and links failure states with unit effects. The analysis of the axial piston unit as a system is made on idealized/theoretical design and functional behavior only. Hence, the failure rating and the effect is subsequently applied to determine the fault risk in form of the Risk Priority Number (RPN). The failure modes and effects are based on engineering experience of past decades, supported by existing DFMEAs of axial piston units. Thus, the assessment of the risk priority number is based on previous data, yielding the given severity, occurrence and detection quantification. This approach opens new opportunities of design assessment and the results show a good agreement to the damage accumulation seen in real field data. Furthermore, the connection between theoretical design assessment and field data do support the failure ranking improvement of the DFMEA.

Stress Analysis of the Cylinder Block in an Axial Piston Pump

“…The FLA and the experimental analysis in [11,12] showed with a high agreement that the cylinder block is the main component related to fatigue relevance in demanding applications. The application and design-specific impact of the cylinder block to an entire system can be seen in Figure 3, where the influencing factor is shown in a failure probability plot in percent.…”

“…As the force can be seen as applied in the tooth centre F HM j ≈ F N HM j , the sum of the forces for every single tooth may be found by summing Equations ( 7), (10), and (11). For the tooth with the j'th position, it yields:…”

“…Therefore, the aim of this work is to develop and evaluate a simplified analysis method concerning material stress applied to the cylinder block splined hub implemented in an axial piston pump. Based on the Failure Likelihood Analysis (FLA) [11,12], previous studies have shown that the cylinder block has a certain fatigue failure probability, implemented in applications with demanding alternating stresses [12]. The cylinder block failure mode covers the splined hub's fractures due to fatigue loading.…”